Electrical conversion system.



' S. GABOT. ELECTRICAL CONVERSION SYSTEM. APPLICATION FILED AUG.10,1911.

- Patented Oct. 6, 1914.

a sna a aaesh J nnnnm SEWALL CABOT, OF BROOKLINE, MASSACHUSETTS.

ELECTRICAL CONVERSION SYSTEM.

Specification of Letters Patent.

Patented Oct. 6, 1914.

Original application filed December 4, 190.), Serial No. 531,306.Divided and this application filed August To all whom it may concern:

Be it known that I, SEWALL CAnoT, a citizen of the United States, and aresident of Brookline, in the county of Norfolk and State ofMassachusetts, have invented a new and useful Improvement in ElectricalConversion Systems, of which the following is a specification.

The invention herein described relates in general to the conversion ofalternating current to direct current and vice versa and specifirally tothe conversion of low potential alternating current to high potentialdirect current and vice .versa. In my application Serial No. 531,300,filed December 4, 1909, upon which Letters Patent 1,081,090 were issuedDecember 9, 1913, I have described systems for converting low potentialdirect current into high potential direct current and vice versa andsystems for converting alternating current into direct current and viceversa, but the claims of the present application, which is a division ofsaid application, are restricted to systems whereby alternating currentis converted into direct current, and vice versa.

I shall describe my invention with reference to the drawings whichaccompany and form a part of this specification and represent in diagramtwo arrangements of apparatus and circuits whereby my object can becarried into effect.

In the drawings,l igure 1 shows in diagram one embodiment of my inention arranged for a' low potential alternating source; Fig. 2 is adiagram showing a modification of the arrangement illustrated in Fig. 1,and Fig. 3 shows a detail of construction.

In the particular drawings selected for more fully disclosing myinvention, E is an alternating current generator or a synchronous motor,according to how it is used, and if a generator, it is a source of lowpoten tial alternating current. current excitation is produced by thesource B, herein shown as a battery, connected with the field-winding F.

I, and I, in Fig. 1 are the low and high potential windings respectivelyof a constant potential type of commercial alternating currenttransformer. However, I do not wish to limit myself to the use of theconstant potential transformer, because it is well understood by thoseversed in the art The usual direct Serial No. 643,322.

that substantially the same result may be effected by an arrangementsuch as shown in Fig. 2, in which'L', I, are the windings of atransformer which may have appreciable magnetic leakage, a portion ofeach winding being out of inductive relation with the other.

Shunted across the terminals of the secondary 'I. in Fig. 1 are theiluluctance L and condenser C. The natural period of the circuit L C maybe made equal to the period of the alternating current supplied by thesource E, so that said circuit will be resonant to the frequency of thealternating current which it is desired to rectify or else the frequencyof the alternating current which it is desired to obtain at thedistributing station by derectification from direct current.

At the points .1 3 is inserted a syncluo nously operating device, suchfor example, as the rotary serially-sululivided switch described in myUnited States Letters Patent 17,749, dated April 13, 1909. whereby thenecessity of resorting to excessively high peripheral velocity isobviated. The principle of this operation is. broadly Sllkilh'lllg, theopening and closing of a circuit by simultaneously iutrmlucing orshunting out a large number of small gaps in series. This apparatus isshown in Fig. 3. in which E is an alternating current generator orsynchronous motor according to how it is used. The device E is assumed,to bc a tour-pole machine generating two cycles for each revolution,when used as a generator or giving one revolution for each two cycleswhen it is operated as a synchronous motor. .\s shown in Fig. 3, therotor 2 is carried by the shaft'J of the device E. \Vhen the dc vice Eis driven by an external source of power, for example, an electric motoror gas engine. alternating current is developed 1n the transformerprimary I, by said device E, which in this case is an alternatingcurrent generator. If, however. no external source of power isconvenient. the. device E may itself be energized by alternating currentof the proper frequency. whereupon itoperates as a synchronous motor,after hav ing first been brought up to the proper speed in any of theusual well known ways. A source of such alternating cur ent of saidproper frequency is represented conventionally by E. When said source Eis used to operate the device E as a synchronous motor, the energy ofsaid source also supplies the transformer I," 1,. It will be understoodof course that the source E may be a generator at a distantly locatedpower sta-,

tion, the mains of which are connected with said device E andtransformer, as shown,

and also tliatan alternating current generator and a synchronous motorare the selfsa'mc piece of apparatus, generating current when actuatedby a source of power and generating power when actuated by a source.

of current, the difference being determined solely by the respectivevalues of the impressed and counter electromotive force at the terminalsthereof. In both cases, i. (2., when the device 'E is an alternatingcurrent generator-developing current or a synchronous motor actuated byalternating current, the rotor 2 is in synchronism with the altermatingcurrent which supplies the transformer primary 1,, and the circuitbetween the points w and y is closed once per cycle.

I may adjust the duration of such closure ,to suit any particularcondition by proportioning the length ofthe members a b and a b, and'Imay cause this closure totake place at the instant the potential of the.

' condenser C isat a maximum ornearly a de-rectification.

. larger the current amplitude of the electrimaximum by adjusting therocker arms 8, 9 with respect to the rotor 2.

of load. This is not possible unless said circuit is made'resonant orapproxi'mately' resonant to the frequency of the current which suppliesthe transformer. Then again, when the device 2 is used for rectifyingalternating current, the use of resonance as aforesaid increases thepower factor of the current drawn from the source, and

Where said I r i used f r (lei-rectifyin direct current, such use ofresonance preserves the sinusoidal character of the wave form of thealternating current obtained by I have found, that the cal oscillations'inthe circuit L C, the closer will be the approach to unity powerfactor and to thefsinusoidal wave form.

" The inductance L is connected in series with the worklng C11Cl1ltwhich may be a transmission line X, and is so propor-' tioned as toprevent current fluctuations in said circuit. The condenser C may beconnected in shunt to said \vorlnng circuit and preferably has a muchlarger capacity than" ing circuit.

the condenser C, so thatit will operate to revent potential fluctuationsin. said work- The arrangement of coils, condensers, etc., connectingthe line X with the distributing station may be'identical with that atthe transmitting station, since the use of electrical resonance rendersthe devicere- In th1s case the device E Isa versible. synchronous motor.energized by the alternating current obtained by the de-rectifica: tionof the direct current received from the line X, and the source E may--be disconnected, or. may be left connected with its terminal voltageadjusted so thatit supplies only sulficient energy to keep the mo-- torE locked into rotation in synchronism with the frequency of said source..As

shown, the apparatus at .the distributing station is identical with thatat the transmitting station and it will be obvious from the precedingdescription that either station may be'used for transmitting or receiving and distributing dependent upon the i ratio of transformation ofthe transform ers at the respective stations. Specifically, the stationshown in the upper part of Fig.

1 may convertv low potential alternating current into very highpotential direct cur-' rent bv means of the step-up transformer I, I theresonant circuit L C and the synchronous commutator rectifier 2, andsaid direct current transmitted over the line X to the distributingstation shown .in the lower part of Fig. 1 where, by. means of thesynchronous cm'nmutatorv de-rectifier 2,. the resonant: circuit L C' andthe step-down transformer I, 1,, said 'highpotential direct .current maybe converted into low potential alternating current in the workingcircuit connected with the motor E, itbeing necessary in this case thattheratio of transa formation "at the distributing station be slightlyless than the 'ratio of transforma tion at the transmitting station ifequal low" potential voltages are desired at both stations, or-else thatthe voltage of the- Y.

source E" at the distributing station be lower than that of the-sourceat the transmittingstation if equal ratios of transfor mation' areemployed -at the two stations. It will be understood of course that anyelectro-responsive device or devices other than a motor may be connectedin said working circuit.

When the natural period of the'circuit L C is equal to the period of thealternating current source, the direction of the electro- ,motive forceon the condenser C 2'. e., the

polarity of'said condenser at the instant of y, will always be the same,and at the no-load condition will be approximately equal *to times therated or R, M. S. voltage on the high potential side of. the

closure of the circuit between the points w,

transformer. Should the potential of the storage condenser C fall belowthis value, energy will be transferred to it from the condenser C in themanner described in my application Serial No. 531,306. Unless energy isbeing drawn from the line X, there can be no transfer of energy from thecondenser C to the storage condenser C and we would then have theno-load condition. During the no-load condition, no energy will passoutward to the working circuit. the impedance of the ircuit I. L C willbe practically infinite and the transformer will take only normalexciting current. (In fact the exciting current may be made less thannormal by a very small increase in the value of L.) The device isreversible and may be made to convert high potential direct currenttransmitted from a distant point over the line X to low potentialalternating cur- .rent, or low potential direct current to highpotential alternating current, that is to say, direct current of eitherhigh or low potential received from the line X may be changed toalternating current of any desired potential in the circuit of theprimary I, by virtue of the rotary switch and interposed resonantcircuit.

In the modification shown in Fig. 2, if the condenser is adjusted to theproper value to make the circuit including the same substantiallyresonant to the frequency of the source, the exciting current at no-loadcondition will have a minimum value which may be made as small asdesirable by keeping the resistance of the transformer windings low.

In putting my invention into practice I make the capacity of thecondenser C such that with the voltage produced by the alternatingcurrent transformer, it will pass the current value desired in theoscillatory circuit L G. Having chosen a condenser of suitable capacity,then if a commercial con stant potential transformer, as in Fig. 1, isused, I adjust the value of the inductance L until the noload orexciting current drawn from the low-potential alternating current sourceis a minimum; but in case a special transformer is designed as in Fig.2, I adjust the turns in the high potential winding until this samecondition is attained. This adjustment insures arriving at the resonantcondition giving best results.

It will be understood that various other modifications may be made inthe arrangement of circuits hereinbefore described without departingfrom the principle of my invention.

I claim:

1. In an electrical conversion system, a source of alternating current,an alternating 'current transformer having one winding connectedtherewith, a condenser connected across the other wmding of Sitldt-IZIIISIOIIDBI,

the circuit including said condenser being resonant to the frequency ofsaid alternating current, a working circuit, and means in synchronismwith said alternating current for conveying energy unidirectionally fromthe resonant circuit to said working circuit.

2. In an electrical conversion system, a source of alternating current,an alternating current transformer having one winding connectedtherewith, a condenser connected across the other winding of saidtransformer, the circuit including said condenser being resmiant to thefrequency of said alternating current, a working circuit, means insynchronism with said alternating current for conveying energyunidirectionally from the resonant circuit to said Working circuit, andan inductance in series with said working circuit for preventing currentfluctuations therein.

3. In an electrical conversion system, a source of alternating current,an alternating current transformer having one winding connectedtherewith, a condenser connected across the other winding of saidtransformer,

the circuit including said condenser be ing resonant to the frequency ofsaid alternatlng current, a working circuit, means in synchronism withsaid alternating current for conveying energy unidirectionally from theresonant circuit to said working circuit, and a capacity in shunt tosaid working circuit for preventing fluctuations of potential therein.

4. In an electrical conversion system, a source of alternating current,an alternating current transformer having one winding connectedtherewith, a condenser connected across the other winding of saidtransformer, a working circuit, and means in synchronism with saidalternating current for conveying energy unidirectionally from saidcondenser to said working circuit.

5. in an electrical conversion system, a

SOIUUc of alternating current, an alternating current transformer havingone winding connected therewith, a condenser connected across the otherwinding of said transformer, a wo:king circuit, means in synchronismwith said alternating current for conveying energy unidirectionally fromsaid condenser to said working circuit, and an inductance in series withsaid working circuit for preventing current fluctuaticns therein.

6. In an electrical conversion system, a source of alternating current,an alternating current transformer having one winding connectedtherewith, a condenser connected across the other winding of saidtransformer, a Working circuit, means in synchronism with saidalternating current for con veying energy unidirectionally from saidcondenser to said working circuit, and 3. capacity in shunt to saidworking circuit for preventing fluctuations of potential therein.

7. In an electrical conversion system, a source of direct current, analternating curv rent transformer associated therewith, a condenserconnected across one' winding of said transformer, the circuit includingsaid condenser being resonant to a definite frequency, a rotary deviceoperatingat said frequency for conveying direct current energy from saiddirect current source to said condenser, and a working circuit connectedto the other winding of said trans former to which alternating currentenergy is delivered. a 8. In an electrical conversion system, a sourceof alternating'current, a circuit energized thereby and resonant to thefrequency thereof, a working circuit and means in synchronism with saidalternating current for conveying energy unidirectionally from said.

resonant circuit to said Working circuit.

.9. In an electrical conversion system, a source of direct current, analternating cur- .rent transformer associated therewith, a

condenser connected across one winding of said transformer, the circuitincluding said condenser being resonant to a definite frequency, arotary device operating at said frequencyfor conveying direct currentenergy from said direct current source .to said condenser, and a workingcircuit connected to the other winding of said transformer.

10. In an electrical conversion system a source of direct current, analternating current transformer associated therewith, a condenserconnected across one winding of said transformer, anon-polarity-changing rotary device for conveying direct current energyfrom said direct current source to said condenser and a working circuitassociated with said transformer. v

11. In an electrical conversion system, a

source of alternating current, an alternating current transformer havingone winding connected therewith, a condenser connected across the otherwinding of said transformer, the circuit including said condenser beingresonant to the frequency of said alternat ing current, a workingcircuit, means in syni chronlsm wlt h said alternating current forconveylng energy unldirectionally from the resonant to a definite"frequency, a rotary device operating at said last mentioned frequencyfor conveying direct current energy from said working circuit to" thelast mentioned condenser, and a working c1rcu1t connected to the otherwinding of the last mentioned transformer.

12. In an electrical conversion system, a source of alternating current,an alternating current transformer having one winding connectedtherewith, a condenser connected across the other winding of saidtransformer, a working circuit, means in synchronism with saidalternating current for conveying energy unidirectionally from saidcondenser to said working circuit, a second alternating currenttransformer associated with said working circuit, a condenser 0on nectedacross one winding of the last mentioned transformer, a rotary devicefor conveying direct current energy from said working circuit to thelast mentioned condenser, and a working circuit associated with the lastmentioned condenser.

4 13. In an electrical conversion system, a course of alternatingcurrent, a step-up transformer associated therewith, a syn chronouscommutator rectifier associated with the 'high potential side of saidtransformer, a synchronous commutator de-rectifier connected to saidsynchronous commutator rectifier, a step-down transformer associatedwith said synchronous commutator de-rectifier, a working circuitassociated SEWALL CABOT.

Witnessesz- Gno. K. WOODWORTH, E. B. 'To nINsoN.

with the low potential side of said step-down

